1. Field of the Invention
The invention relates to a jitter measuring method and device, and more particularly to a jitter measuring method and device for precisely calculating the length of a serial digital signal according to a multi-phase clock to measure the jitter correctly.
2. Description of the Related Art
In an optical storage apparatus, a jitter measuring device (jitter meter) is an important device. The measurement result of the jitter measuring device is an indicator for the signal quality. If a jitter measuring device with precise result is employed in the optical storage apparatus, the optical storage apparatus can acquire correct signal information and adjust itself to an optimum state. The jitter measuring method is typically divided into a digital method and an analog method.
The digital method includes the steps of shaping the serial digital signal, calculating the number of pulses of a reference clock for each pulse of the shaped signal, and then finding out a difference value between the calculated numbers as the jitter value. The drawbacks of this method are that it is necessary to provide the reference clock with higher frequency if the frequency of the serial digital signal is high.
The analog method includes the steps of converting each pulse width of the serial digital signal into an analog signal, and then filtering the voltage of the analog signal by a filter. The filtered voltage variation represents the jitter value. The drawbacks of this method are that the switching speed of the used switches may greatly influence the measurement result, and the switches with a high switching speed cannot be easily implemented.